Gaseous electric discharge device



Dec. 21, 1937. P. SCHOONENBERG ET AL 2,103,043

GASEOUS ELECTRIC DISCHARGE DEVICE Filed July 22, 1935 INVENTORS ATTORNEY stamina ec. i, E93? mtt t Pancras schoonen berg and Josephus A. M. Smelt, I Eindhoven, Netherlands, assignors to General Electric Company, aeorporation of New York Application July 22, 1935, Serial No. 32,608

v In Germany July 26, 193i 3 Claims. The present invention relates to gaseous electric discharge devices generally and more particularly the invention relates-to. such devices the gaseous atmosphere of which consists of or comprises the vapor of an alkali metal, such as sodium.

The usual container glasses for incandescent lamps or gaseous discharge lamps, such, as lime glass, lead glass, soda glass, or the like are not suitable for use as container glasses for alkali vapor lamps since these glasses are rapidly blackened "by the alkali metal vapor. Attempts have been made-to supply a glass suitable for use as a containerglass for alkali vapor lamps. One type of glass proposed contained no silica and had a large content of boric oxide together with one or more ofthe oxides of alkalies, alkali earths,

, aluminum and magnesium. While'this glass successfully resists the destructive action of alkali metal vapor it isdifiicult to work and is hygroscopic.

More recently a 'boro-silicate' glass has been proposed which contains an appreciable amount of silica. A typical composition of such glass is thefollowing v Per cent Sodium oxide (NazO) 4to 5 Aluminium oxide (AlzOs) 11 to 13 Calcium oxideiCaO) 10 to 11 Boric oxide (B203) 40 to 60 Silica (Siz) 10 to 25 The hero-silicate glass is less hygroscopic than the boric oxide glass, is readily workable and a many sodium lamps having containers made of this glass have been manufactured.

We have observed however, that the above boro-silicate glass cannot be successfully used as the container glass for alkali vapor lamps having a positive column discharge with a large voltage gradient and a large current density. This type of vapor latnp is a highly efiicient light source but prior to our discovery was not available in commerce since theeasily workable, vapor resistant, boro-silicate glasses successfully used in other types of alkali vapor lamps become blackened after the lamps of the positive column type have been operating a short time. Our explanation for this phenomenon is that in this type of lamp the large voltage gradient is accompanied by high electron velocity which in turn in the vicinity of the thin lateral field are attracted thereby and strike the inner surface of 5 the container. at high velocity. This heavy ionic bombardment causes discoloration of the glass which reduces the light out-put, particularly when the current density is high. The useful life of such alamp is so short as to'be infeasible commercially. This is particularly true when the voltage gradient is greater than 2.2 volts per cm. and the current density is higher than 0.4 ampere per cm We have discovered that a 'boro-silicate glass 15 containing less than 10% of silica, does not blacken when used on the inner surface of the container of a gaseous electric discharge lamp of the positive column type which has avoltage gradient greater than 2.2 volts per cm. along the .positive column discharge. and a current density greater than 0.4 ampere per cm. We have also discovered that the resistance of the glass to blackening increases as the silica content thereof decreases. When the voltage gradient and the current density is greater than the values given above the silica content of the glass is preferably less than 10%. Since the silica makes theglass workable it is desirable that the glass contain some silica.

. In the drawing accompanying and forming part of this specification a gaseous electric discharge lamp embodying the present invention is shown schematically.

Referring to the drawing the lamp comprises mionic electrode 2 sealed into each end thereof.

Each of said electrodes 2 consists of a heater filament, such as a tungsten filament, in operative relation to .a body of electron emitting material, such as a coating of barium oxide. Said container has a rare starting gas therein,-such as neon at a pressure of 10 mm. and a small percentage of argon, and a quantity of sodium therein the vapor of which is light emitting during the operation of the lamp. The internal diameter of the parallel legs of said container I is 12.5 mm. and the distance between the electrodes 2 is 62 cm. measured along the axis of the container I. The operating voltage of the lamp is 2 approximately 1'70 volts and the current density is approximately 0.6 ampere. The voltage gradi ent' along the positive column is 2.66 volts per cm. and the current density is approximately 0.5 ampere per cm. A glass of the following composition does not becomeblackened in a lamp of this type and the lamp has a long useful operating life:

Per cent Silica (SiOz) 6 Boric oxide (B203) 53 Aluminium oxide (Al-203) 15 Calcium oxide (CaO) 10 Sodium oxide (NazO) 16 We prefer to make the container I of flashed glass, that is, the container I consists of two glass layers the outer layer being of one of the usual container glasses, well known in the art,

and the inner layer of an alkali vapor resistant glass having the above composition.

While we have shown and described and have pointed out inthe annexed claims certain novel features of the invention, it will be understood that various omissions, substitutions and changes in the forms and details of thedevice illustrated and in its use and operation may be made by thoseskilled in theart'without departing from the spirit and scope-of the invention.

. what we claim as new and desire to secure by Letters Patent of the United States, is:-

. 1. In combination a gaseous electric discharge device of the positive column type comprising a container, electrodes, sealed therein, a gaseous atmosphere therein-comprising an alkali metal vapor, and means to supply sumcient electrical energy to said device to cause a voltage drop along the positive column discharge greater than 2.2 volts per cm. and a current density in said discharge greater than 0.4 ampere per cmfi, the inner surface of said container being of a boro- Percent Silica (S102) 6 Boric oxide (B203) 53 Aluminium oxide (AlzOa) 15 Calcium oxide (CaO) 10 Sodiumoxide (NazO) 16 3. In combination a gaseous electric discharge device of the positive column type comprising a container, electrodes sealed therein, a gaseous atmosphere therein comprising an alkali metal vapor, and means to supply sufllcient electrical energy to said device to cause a voltage drop along the positive column discharge of approximately 2.66 volts per cm. and a current density in said discharge of approximately 0.5 ampere.

per cm the innersurface of said container being of a glass having the following composition:--

' Percent Silica (SiOz) 6 Boric oxide (B203) 53 Aluminium oxide (A1203) 15 Calcium oxide (CaO) 10 Sodium oxide (NazO) 16 PANCRAS SCHOONENBERG. JOSEPHUS A. M. SMELT. 

